Highly nucleated syndiotactic polypropylene

ABSTRACT

The present invention relates to methods of producing syndiotactic polypropylene articles through high performance nucleation via the presence of certain novel nucleating agents within molten syndiotactic resins, and subsequently permitting the resultant molten mixture to cool into a selected shape or configuration. Such novel nucleating agents are new classes of hyper-nucleators that promote crystallization within such target syndiotactic resins at levels well above any previously disclosed nucleators. This invention thus also encompasses the articles and compositions of such nucleated syndiotactic polypropylene as well.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending application Ser. No.10/121,224, filed on Apr. 12, 2002, now U.S. Pat. No. 6,703,434, whichis a continuation of application Ser. No. 10/121,400, filed Apr. 12,2002, now U.S. Pat. No. 6,642,290. This parent application is hereinentirely incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to methods of producing syndiotacticpolypropylene (s-PP) articles through high performance nucleation viathe presence of certain novel nucleating agents within moltensyndiotactic resins, and subsequently permitting the resultant moltenmixture to cool into a selected shape or configuration. Such novelnucleating agents are a new class of nucleators that promotecrystallization within such target syndiotactic resins at levels wellabove any previously disclosed nucleators. This invention thus alsoencompasses the articles and compositions of such syndiotacticpolypropylene as well.

BACKGROUND OF THE PRIOR ART

All U.S. patents cited below are herein entirely incorporated byreference.

Polypropylene has long been known to exist in several forms. Generally,isotactic propylene (iPP) can be described as having the methyl groupsattached to the tertiary carbon atoms of successive monomeric units onthe same side of a hypothetical plane through the polymer chain, whereassyndiotactic polypropylene (sPP) may generally be described as havingthe methyl groups attached on alternating sides of the polymer chain.More specifically, the isotactic structure is typically described ashaving the methyl groups attached to the tertiary carbon atoms ofsuccessive monomeric units on the same side of a hypothetical planethrough the main chain of the polymer, e.g., the methyl groups are allabove or all below the plane. A more thorough description ofsyndiotactic polypropylene is found in col. 1, line 19 of col. 3 of U.S.Pat. No. 5,969,021 to Reddy et al., particularly in comparison with thegeneral configurations of isotactic polypropylene.

Thus, syndiotactic polymers, in contrast to the isotactic structure, arethose in which the methyl groups attached to the tertiary carbon atomsof successive monomeric units in the chain lie on alternate sides of theplane of the polymer, thereby creating a configuration of successivemethyl groups on alternate sides of a common plane (i.e., racemicdyads). The percentage of racemic dyads in the chain thus determines thedegree of syndiotacticity of the polymer. Syndiotactic polymers arecrystalline and, like the isotactic polymers, are insoluble in xylene(although the degree of crystallinity of s-PP is much less than fori-PP). This crystallinity distinguishes both syndiotactic and isotacticpolymers from an atactic polymer which is amorphous, and soluble inxylene. Atactic polypropylene exhibits no regular order of repeatingunit configurations in the polymer chain and forms essentially a waxyproduct. Furthermore, s-PP exhibits a far lower melting point (˜128° C.)than for i-PP (˜153-170° C.).

Such noticeable physical differences in comparison with i-PP allow forutility of s-PP in specialized applications. For example, syndiotacticpolypropylene provides such improved characteristics over isotactictypes, namely, but not limited to, clarity, toughness (impactresistance), and feel (softness), as well as surface smoothness anduniformity, some improvements to an extraordinary degree. Thus, end-usessuch as dental retainers, medicine droppers, eye droppers, and pen capsnormally include s-PP as the primary polymer. However, historicutilization of such a polymer within other fields has been severelylimited due to problems associated with low crystallization rates andcrystallization temperatures (and thus inordinate cost levels), as wellas low flexural modulus characteristics.

As noted within the citation to Reddy et al., above, the crystallizationrate of syndiotactic polypropylene is much slower than that forisotactic PP due the low retention rate of crystallinity exhibited bysyndiotactic polypropylene in general. In fact, syndiotacticpolypropylene continues to crystallize even after pelletization thereofduring the production of the resin throughout the process. Furthermore,such low crystallization temperatures also require cooling of injectionmolded parts or extruded films or sheets to much lower temperatures, andin some cases, higher than needed, for example, for isotacticpolypropylene, thereby adding to the cost of manufacture as well due toslower production rates and increased energy costs. Additionally, notonly does syndiotactic polypropylene have crystallization temperaturesand rates that could be improved, some common processing additives, suchas calcium stearate, tend to reduce the crystallization rate even more.

Such slow crystallization rates are generally attributable to the factthat syndiotactic polypropylenes exhibit polymorphism; that is, threedifferent crystal types, namely cell I, cell II, and cell III structurestherein. Due to the inherent similarities between Cell I and Cell III,only Cell III will be referred to hereinafter. It has been traditionallynoted that the manufacture of syndiotactic polypropylene requires twodistinct steps after melting of the target resin in order for thecrystal structures to change from one structure to another and finallyto the desired final type (cell II). The initial crystal configuration,known as cell II (which includes anti-chiral helices along the “a”crystallographic axis and chiral helices along the “b” axis), appearsquickly during cooling and is kinetically favored. The cell III crystalstructure (which includes anti-chiral helices along both the “a” and “b”crystallographic axes) then forms at relatively high temperatures(thermodynamically favored) during cooling of the molten resin form.Such a cell III structure for syndiotactic polypropylene (highermelting), although formed more slowly, is always in competition with theCell II form (lower melting), and is not desirable since it is arubbery, opaque phase and cannot be pelletized during processing. Inorder to effectuate proper cell II formation, generally such rubberycell III-type s-PP must then, in general non-limiting terms, be extrudedinto strands and wound around a spool to permit further cooling and thusgeneration of the necessary rigidifying cell II configuration. Thus, itappears that the crystallization rate of syndiotactic polypropylene isdictated by the amount of cell III crystals present and thus requiringgeneration and arrangement within the target polymer. Without intendingon being limited to any scientific theory, it appears that proper anduseful syndiotactic polypropylene articles should include higher amountsof the rigid cell II crystal types. The apparent problem in the pastwith slow crystallization procedures lies in the presence of largeamounts of cell III crystals therein. A lower amount of such cell IIIcrystal types would thus permit more thorough crystallization of theoverall syndiotactic polypropylene during the initially formed cell IIphase, thereby reducing the amount of time required for fullcrystallization thereof. As a result, it is believed that a syndiotacticpolypropylene production method that generates higher amounts of cell IIcrystal structures than cell III types would exhibit fastercrystallization (or at least higher crystallization temperatures) andthus would reduce the cost and complexity associated with producingsyndiotactic polypropylene articles. In effect, then, such an improvedmethod would permit more widepread use of such an excellent performingclass of polypropylenes. As it is today, the dichotomy in melting formsbetween cell II and III crystal structures causes a processing problemin terms of complexity and time and thus such syndiotactic polypropylenetypes have proven very difficult to efficiently produce, even withcertain nucleating agents present. Thus, as noted above, the needappears to be to reduce the amount of cell III present therein, thuspermitting the cell II component to dictate polymer formation,preferably wherein more cell II form is produced than cell III crystals.Furthermore, it appears that a reduction in the amount of rubbery cellIII crystals within target s-PP formulations leads to the formation ofmore flexurally stable end-product articles as well (e.g., the fewerrigid cell III crystals are present, the polypropylene tends to be moreflexible and less susceptible to breaking). Unfortunately, to date nosuch specific advancement has been proffered to the syndiotacticpolypropylene industry wherein the majority of s-PP crystals are CellII.

Thus, in spite of the advancements in the prior art relating tosyndiotactic polypropylene, there is a need for a method of improvingthe crystallization rate and temperature of syndiotactic polypropylene,in addition to the stiffness of final s-PP articles. As a result, then,there is also a need in the art for improving such characteristics,particularly in order to allow for utility of s-PP within larger marketareas, particularly those which are today dominated by isotacticpolypropylene. To date, no such advancements have been made availableincreasing the crystallization rates of syndiotactic polypropylene tolevels acceptable to displace isotactic polypropylene as the basepolymer in certain end-uses.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide for a method ofimproving the crystallization rate and temperature of syndiotacticpolypropylene. It is another object of the present invention to providefor a syndiotactic polypropylene having improved crystallization rateand temperature of syndiotactic polypropylene. It is even another objectof the present invention to provide for products made from syndiotacticpolypropylene having improved crystallization rate and temperature ofsyndiotactic polypropylene.

Accordingly, this invention encompasses a method of treatingsyndiotactic polypropylene comprising the step of compoundingsyndiotactic polypropylene with at least one compound selected from thegroup consisting of compounds conforming with either of formulae (I) or(II)

wherein M₁ and M₂ are the same or different or are combined to form asingle moiety and are selected from at least one metal cation (such as,without limitation, sodium, potassium, calcium, strontium, lithium, andmonobasic aluminum), and wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, andR₁₀ are either the same or different and are individually selected fromthe group consisting of hydrogen, C₁-C₉ alkyl [wherein any two vicinal(neighboring) or geminal (same carbon) alkyl groups may be combined toform a carbocyclic ring of up to six carbon atoms], hydroxy, C₁-C₉alkoxy, C₁-C₉ alkyleneoxy, amine, and C₁-C₉ alkylamine, halogens(fluorine, chlorine, bromine, and iodine), and phenyl, wherein geminalconstituents may be the same except that such geminal constituentscannot simultaneously be hydroxy; and wherein geminal constituents maybe different from each other, except that such geminal constituents maynot be hydroxy and halogen or hydroxy and amine simultaneously;

wherein R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆, R₁₇, R₁₈, R₁₉, and R₂₀ areindividually selected from the group consisting of hydrogen, C₁-C₉alkyl, hydroxy, C₁-C₉ alkoxy, C₁-C₉ alkyleneoxy, amine, and C₁-C₉alkylamine, halogen, phenyl, alkylphenyl, and geminal or vicinal C₁-C₉carbocyclic, wherein geminal constituents may be the same except thatsuch geminal constituents cannot simultaneously be hydroxy; and whereingeminal constituents may be different from each other, except that suchgeminal constituents may not be hydroxy and halogen or hydroxy and aminesimultaneously; wherein R′ and R″ are the same or different and areindividually selected from the group consisting of hydrogen, C₁-C₃₀alkyl, hydroxy, amine, polyoxyamine, C₁-C₃₀ alkylamine, phenyl, halogen,C₁-C₃₀ alkoxy, C₁-C₃₀ polyoxyalkyl, C(O)—NR₂₁C(O), and C(O)O—R′″,wherein R₂₁ is selected from the group consisting of C₁-C₃₀ alkyl,hydrogen, C₁-C₃₀ alkoxy, and C₁-C₃₀ polyoxyalkyl, and wherein R′″ aloneor two adjacent R′″ groups (such as when R′ and R″ are the same) arecombined to from a single moiety which is selected from the groupconsisting of hydrogen, a metal ion (such as, without limitation,sodium, potassium, calcium, strontium, lithium, and monobasic aluminum),an organic cation (such as quaternary amines), polyoxy-C₂-C₁₈-alkylene,C₁-C₃₀ alkyl, C₁-C₃₀ alkylene, C₁-C₃₀ alkyleneoxy, a steroid moiety,phenyl, polyphenyl, C₁-C₃₀ alkylhalide, and C₁-C₃₀ alkylamine; andwherein at least one of R′ and R″ is either C(O)—NR₂₁C(O) or C(O)O—R′″.The term “monobasic aluminum” is well known and is intended to encompassan aluminum hydroxide group as a single cation bonded with the twocarboxylic acid moieties. Furthermore, for Formula I, in each of thesepotential compounds, the stereochemistry at the metal carboxylates maybe cis or trans, although cis is preferred. In Formula II, thestereochemistry at the R′ and R″ groups may be cis-exo, cis-endo, ortrans, although cis-endo is preferred.

According to still another potential embodiment of the presentinvention, there is provided a method of forming a product including thestep of heating a mixture comprising syndiotactic polypropylene and anadditive above the melt temperature of the syndiotactic polypropylene toform a melted mixture, wherein the additive comprises at least oneselected from the group consisting of compounds of either Formula (I) or(II), or mixtures thereof. The method also includes the step of formingthe melted mixture into a desired shape, particularly a method whereinthe shaped article is formed by cooling the desired shape to below themelt temperature of the syndiotactic polypropylene.

Further encompassed within this invention is a syndiotacticpolypropylene article (wherein the definition of syndiotacticpolypropylene can include the presence of up to about 30 weight percentisotactic, atactic, or mixtures thereof, polypropylene types),exhibiting a peak crystallization temperature (peak T_(c)) of at least71° C., preferably at least about 74° C., when measured via differentialscanning calorimetry (DSC) under a modified version of ASTM Test MethodD-794-85, wherein the sample is cooled at a rate of 20° C. per minute,or alternatively, exhibits the same high peak crystallizationtemperature as well as a flexural modulus of at least 900 MPa asdetermined according to ASTM Test Method ASTM D790-98, procedure B.Lastly, this invention also encompasses a syndiotactic polypropylenethat exhibits a greater amount of cell II crystal structures incomparison with cell III crystal structures within the same finalpolymer product, as measured via DSC analysis.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, in order to develop a proper high crystallizingsyndiotactic propylene to permit widespread commercial applications ofsuch a unique polymer, a novel nucleating technology was developed thatunexpectedly produces a range of amounts of cell II (lower melting)crystal formations from a slight excess to much greater levels incomparison with the amount produced of the cell III (higher melting)types. Surprisingly, such novel nucleators as noted below not onlygenerated such greater amounts of higher cell II crystal structures,they also provided higher, and in some cases, extremely highercrystallization temperatures for target syndiotactic polypropylenes. Asa result, efficiency has been increased and complexity has been reducedin relation to unnucleated syndiotactic polypropylene during processing.Also, such novel nucleators are compatible with common syndiotacticpolypropylene additives.

Such inventive nucleating procedures thus encompass the addition ofcertain types of bicyclic or monocylic dicarboxylic acid salts ormono-salts (half-acid, half salt) compounds, noted above in terms ofFormulae (I) or (II). The non-limiting preferred type of nucleatingadditive is a monocyclic diacid salt (such as cis-calciumhexahydrophthalate) that induces a peak crystallization temperature inexcess of 74° C. for syndiotactic polypropylene containing about 70-80%racemic dyads. As noted below within the examples, such a highcrystallizing nucleating procedure is a highly unexpected improvementover the standard procedures utilizing NA-11 as the standard nucleator.With the cost of such polypropylene already quite high (due to itsmanufacture via expensive metallocene catalysis), the utilization ofsuch syndiotactic types have been avoided. The ability now to increasethe efficiency of processing of such a specific polypropylene thustranslates into not only lower costs to the consumer, but also theability to potentially enter markets previously unavailable to suchexcellent polypropylene formulations and articles.

The syndiotactic polypropylene utilized in the present invention, andmethods of making such a syndiotactic polypropylene, are well known tothose of skill in the polyolefin arts. An example of a suitablesyndiotactic polypropylene and a method of its making can be found inU.S. Pat. Nos. 4,892,851, 5,334,677, and 5,476,914, all herein entirelyincorporated by reference.

Preferably, the syndiotactic polypropylene utilized in the presentinvention comprises tacticity of at least 70 percent racemic dyadmolecules as defined by the percent of racemic dyads (i.e., an amount ofisotactic or other type of non-syndiotactic polypropylene of at mostabout 30 weight percent). It is foreseen that desired syndiotacticpolypropylene utilizing the inventive nucleation techniques willcomprise syndiotacticity of at least 80 percent racemic dyads, even morepreferably at least 83 percent racemic dyads, and still more preferablyat least about 90 percent racemic dyads. Most preferably, such foreseensyndiotactic polypropylenes utilizing the present inventive nucleationtechniques would consist of all syndiotactic molecules.

The syndiotactic polypropylene useful in the present invention willgenerally be selected according to the desired end use of polypropylene,for compatibility with the additives, and for compatibility with theprocessing conditions, and with any other polymers to be added thereto.

As a non-limiting example, a suitable syndiotactic polypropylene whichmay be utilized in the present invention may generally be described ashaving a number average molecular weight in the range of about 30000 toabout 150000, a weight average molecular weight in the range of about60000 to 350000, a melting point in the range of about 95° C. to about165° C., a bulk density in the range of about 0.28 to about 0.55 g/cc,polymer density in the range of about 0.87 to 0.90 g/cc, polydispersityin the range of about 2 to about 5, and a percent racemic dyad valuebetween about 70-74 percent.

The particular compounds noted above, as proper nucleating agentspresent within such syndiotactic polypropylenes include any compoundencompassed within the Formulae of (I) or (II), as defined above indetail. Preferably, for Formula (I), all of the R groups are hydrogenand the M groups are combined to form a calcium ion. For Formula (II),all the R groups, except R′ and R″, are hydrogens, and both R′ and R″are carboxylic acids with the R′″ groups individual sodium ions.

Such aforementioned nucleation properties within syndiotacticpolypropylene are highly unexpected and unpredictable, particularly inview of the closest prior art, namely within U.S. Pat. No. 3,207,739 toWales, as well as within Beck, H. N., “Heterogeneous Nucleating Agentsfor Polypropylene Crystallization,” Journal of Applied Polymer Science,Vol. 11, pp. 673-685 (1967), which disclose disodium hexahydrophthalateas a possible, though not preferred, nucleator for polymers (suchdisclosures are directed more specifically to sodium benzoate and otherlike aromatic compounds as better nucleators), and WO 98/29494 whichdiscloses nucleation and clarification additives for polyolefin articlesincluding unsaturated [2.2.1] dicarboxylate salts; however, there is noexemplification of a saturated dicarboxylate (or similar saturatedstructure) of this type (other than heterocyclic camphanic acid). Theclosest embodiment within that art is identified as disodiumbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate. None of these referencesdiscuss any nucleation advantages for the taught compounds in relationspecifically to syndiotactic polypropylene to the degree hereinrealized. Most notably, the utilization of such compounds as noted aboveprovide highly unexpected improvements in crystallization rates andtemperatures, as well as stiffness and, perhaps, most importantly, theamount of cell II crystals formed within the target polymer in relationto the amount of cell III crystals therein. Again, the aforementionedprior art references fail to provide any motivation for the introductionof such compounds as encompassed within Formulae (I) and/or (II), above,within syndiotactic polypropylene. Thus, after intensive investigations,it has been determined that, quite unexpectedly, as discussed below ingreater detail, the utilization of certain preferred, and non-limiting,metal hexahydrophthalates, and, to a lesser extent, the utilization ofnucleating compounds produced through the hydrogenation of unsaturatedbicyclic carboxylic acid salts, provide vastly improved nucleationresults for syndiotactic polypropylenes to a level heretoforeunattainable, particularly at a commercially viable level. As indicatedin Table 1, below, as one example of this phenomenon, the peakcrystallization temperatures provided the inventive syndiotacticpolyolefin articles are from about 1 to as high as about 6° C. abovethat for the standard, previously best performing syndiotactic nucleatorcompounds. Such dramatic improvements are simply unexpected and areunpredictable from any known empirical or theoretical considerations andare of great practical significance as discussed before.

As noted above, proper nucleator compounds for industrial applicationsrequire a number of important criteria to be met, such as shelfstability, particularly in terms of low hygroscopicity, high finalarticle stiffness, gas barrier properties, and plastic additivecompatibility, such as stability in combination with acid scavengers,such as calcium stearate, for example. The compounds noted above inFormulae (I) and (II) appear to meet all of these important requirementsvery well. For instance, these inventive compounds do not hydratereadily and thus granular or powder formulations of such a salt do notagglomerate or clump together. The cost benefits from such shelfstability are apparent since there is little if any need to separateagglomerated powders upon introduction to thermoplastic processingequipment. Additionally, such nucleating salts provide high stiffness(modulus) characteristics to the overall final syndiotactic polyolefinproduct without the need for extra fillers and reinforcing agents,although such potentially unnecessary additives may be added if such aredesired to improve the target properties therein. Lastly, and of greatimportance within the polypropylene industry, such inventive salts donot react deleteriously with calcium stearate co-additives. Such aproperty, combined with the other attributes, is highly unexpected andunpredictable.

The HHPA and/or bicyclic salts of Formula (I) and/or (II), above, arethus added within the target syndiotactic polypropylene in an amountfrom about 0.01 percent to 5.0 percent by weight, more preferably fromabout 0.02 to about 3.0 percent, and most preferably from about 0.05 to2.5 percent, in order to provide the aforementioned beneficialcharacteristics (1.0% by weight equals about 10,000 ppm). It may also bedesirable to include up to 50% or more of the active compound in amasterbatch, although this is not a restriction. Optional additiveswithin the nucleating salt-containing composition, or within the finalthermoplastic article made therewith, may include plasticizers,stabilizers, ultraviolet absorbers, and other similar standardthermoplastic additives. Other additives may also be present within thiscomposition, most notably antioxidants, antimicrobial agents (such assilver-based compounds, preferably ion-exchange compounds such asALPHASAN® antimicrobials from Milliken & Company), antistatic compounds,perfumes, chloride scavengers, and the like. These coadditives, alongwith the nucleating agents, may be present as an admixture in powder,liquid, or in compressed/pelletized form for easy feeding. The use ofdispersing aids may be desirable, such as polyolefin (e.g.,polyethylene) waxes, stearate esters of glycerin, montan waxes, andmineral oil. Basically, the nucleating compounds may be present (up to20% by weight or more) in any type of standard additive form, including,without limitation, powder, prill, agglomerate, liquid suspension, andthe like, particularly comprising the dispersing aids described above.Compositions made from blending, agglomeration, compaction, and/orextrusion may also be desirable.

Non-limiting commercially available products suitable for use in thepractice of the present invention, in addition to the inventivenucleators noted above, include Millad® 3988 (3,4-dimethyldibenzylidenesorbitol), available from Milliken Chemical, NA-11® (sodium2,2-methylene-bis-(4,6,di-tert-butylphenyl)phosphate))), available fromAsahi Denka Kogyo, and aluminumbis[2,2′-methylene-bis-(4,6-di-tert-butylphenyl)phosphate], which ishereinafter referred NA-21®, also available from Asahi Denka Kogyo.

The crystallization additive or additives may be added to thesyndiotactic polypropylene during or after polymerization. Preferably,it is added to the syndiotactic polypropylene as it is being extrudedthrough the extrusion die.

In the present invention, the syndiotactic polypropylene treated withthe crystallization additive, will have a peak crystallizationtemperature that is improved as compared to the untreated syndiotacticpolypropylene. Generally, the peak crystallization temperature of thetreated syndiotactic polypropylene is in excess of about 71° C. (forsyndiotactic polypropylene comprising about 70-75% syndiotacticity),preferably in excess of about 74° C. (for syndiotactic polypropylenecomprising about 70-75% syndiotacticity), most preferably in excess ofabout 77° C. (by DSC analysis when a cooling rate of 20° C./minute isused).

The syndiotactic polypropylene crystallized according to the presentinvention will also have an increased content of cell II (low meltingform) structure and a decreased content of cell III (high melting form)such that the amount of cell II at least about the same in amount asthat of cell III (such as low as about 45% cell II correlated to about55% cell III, although higher amounts of cell II are more highly desiredfor crystallization and manufacturing speed improvements).

Non-limiting examples of possible reinforcing agents which may be addedto the target syndiotactic polypropylene include inorganic or organicproducts of high molecular weight, including glass fiber, asbestos,boron fibers, carbon and graphite fibers, whiskers, quartz and silicafibers, nanocomposites (such as Montmorillonite clays), and syntheticorganic fibers. When such conventional ingredients are utilized, theywill generally be present in a range from about 0.01 to about 50 weightpercent of the blend, preferably in a range from about 1 to about 25weight percent of the blend.

PREFERRED EMBODIMENTS OF THE INVENTION

The following Examples are provided merely to illustrate selectedembodiments of the present invention and do not limit the scope of theclaims.

Production of Inventive Salts

EXAMPLE 1 Cis-Calcium Hexahydrophthalate

To an 8-L cylindrical kettle fitted with a mechanical paddle stirrer andthermometer was added water (4 L) and calcium hydroxide (481 g, 6.49moles) with stirring at room temperature. To this slurry was addedcis-hexahydrophthalic anhydride (1 kg, 6.49 moles) and the slurry washeated to 50° C. After stirring with heat for 5 hours, the mixturebecame quite thick, at which time the pH of the aqueous phase was foundto be about 7. The white product was collected by suction filtration,washed with copious amounts of water, dried in a vacuum oven overnightat 140° C., and further air-jet milled to provide a powder of roughlyuniform particle sizes. The dry weight was 1270 grams (93% yield) havinga melting point greater than about 400° C. The IR spectrum wasconsistent with that of the expected product.

EXAMPLE 2 Disodium bicyclo[2.2.1]heptane-2,3-dicarboxylate

To a solution of disodium bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate(10.0 g) in water (100 g) was added 0.5 g palladium on activated carbon(5 wt %). The mixture was transferred into a Parr reactor and wassubjected to hydrogenation (50 psi, room temperature) for 8 hours. Theactivated carbon was filtered out, and the water was removed in vacuo at75° C. The resulting product (m.p>300° C.) was dried and milled. NMR andIR analyses were consistent with that of the expected structure.

Base Polymers

The base s-PP fluff used for compounding had a racemic dyad content ofbetween 70 and 80% and a MFR of about 4 g/10 min., and was unstabilizedas received. For stabilization, it was compounded with an antioxidantpackage containing 500 ppm Irganox® 1010 (CibaGeigy){tetrakis-(methylene[3,5-di-tert-butyl-4-hydroxyhydrocinnamate]methane)}and 1000 ppm Irgafos® 168 (Ciba Geigy), plus the individual nucleatingagents, either inventive or comparative in nature, as noted below.Calcium stearate (CaSt) was used at 800 ppm as the acid-acceptor, exceptin the case of NA-11 and sodium benzoate (NaBz), wherein dihydrotalcite(DHT4-A, Kyowa Chemical) was used at a level of 400 ppm. The compoundedfluff was mixed thoroughly in a Welex mixer and extruded on a Prism 16mm twin-screw microextruder into strands. The strands were cooled on aspool to room temperature and pelletized using a laboratory pelletizer.Extrusion conditions were as follows: Zone 1, 370° F., Zone 2, 415° F.,Zone 3, 435° F., and Zone 4 (die), 455° F. 1 kg batches of pellets werethus made in this manner.

Testing for nucleating effects and other important criteria wereaccomplished through the formation of 50 mil plaques from the pelletizedsyndiotactic polypropylene thermoplastic resin. The plaques were moldedon an Arburg (20 ton) press using a barrel temperature of 205° C. and amold temperature held at 100° F. It was observed that for theunnucleated control resin, the plaque crystallization was characterizedby a hazy, rubbery phase which gradually transformed into a clear, rigidphase. The minimum cycle time for these plaques was thus determined tobe the minimum time required to eject a transparent plaque withoutwarpage of the part on further cooling. These plaques were formedthrough the process outlined above with the specific nucleating agentslisted in the Table below.

These plaque formulations are, of course, merely preferred embodimentsof the inventive article and method and are not intended to limit thescope of this invention. The resultant plaques were also tested for peakcrystallization temperatures (by Differential Scanning Calorimetry, orDSC) with a 20° C./min. cooling rate. Generally, a polyolefin such asunnucleated syndiotactic polypropylene has a peak crystallizationtemperature of about 60-70° C. at most on cooling when comprised ofabout 70-80% racemic dyads and when measured at a DSC cooling rate of20° C./min. In order to reduce the amount of time needed to form thefinal product, as well as to provide the most effective nucleation forthe polyolefin, the best nucleator compound added will invariably alsoprovide the highest crystallization temperature for the finalsyndiotactic PP product. The nucleation composition efficacy, particularpolymer onset and peak crystallization temperature (T_(c)), wasevaluated by using DSC according to ASTM D-794-85. To measure thesetemperatures, the specific syndiotactic polypropylene compositionslisted below were heated from 25° C. to 220° C. at a rate of 20° C. perminute to produce a molten formulation and held at the peak temperaturefor 2 minutes. At that time, the temperature was then lowered at a rateof 20° C. per minute until it reached the starting temperature of 25° C.The crystallization temperature was thus measured as the peak maximumduring the crystallization exotherm. The clarification performance ofthe nucleators was measured using ASTM D 1003-92. The stiffness of eachsample was measured in accordance with ASTM D790-98, procedure B.

Table 1 below lists the onset and peak crystallization temperatures,haze measurements, and flexural modulus results for the plaques preparedabove:

EXPERIMENTAL TABLE 1 Performance of Nucleators in SyndiotacticPolypropylene Additive Cryst. Temp. Cryst. Temp. Flexural NucleatorsConc. (%) Onset (° C.) Peak (° C.) Modulus (MPa) Haze (%) Example 1 0.2595 77 944 16 Example 2 0.25 76 71 955 14 Sodium Benzoate 0.1 70 64 84423 NA-11 0.1 70 65 870 9 3,4-DMDBS 0.25 71 63 830 6 None — 70 60 790 13

The data shows that the inventive nucleators, and thus the inventivesyndiotactic propylene, exhibit significantly higher polymer onset andpeak crystallization temperatures and flexural modulus measurements thanfor the comparative nucleators. In addition, the clarity of thecompositions is not drastically affected when Example 1 and 2 are usedin the formulation.

To determine the relative amounts of Cell II and Cell III crystalstructures within each tested formulation, the first melting transitionswere observed after injection molding. The Cell II form melts at about115° C., while the Cell III form melts at about 126° C. on heating at20° C./minute. The combined DSC thermograms are shown FIG. 1.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a DSC Thermogram of melting transition of syndiotacticpolypropylene with various nucleating agents, as listed.

DETAILED DESCRIPTION OF THE DRAWING

In FIG. 1, there is supplied the thermogram for which the amounts ofdifferent cell II and cell III crystal structures were formed in variousnucleation systems. Such systems are noted in terms of the nucleatorsutilized. The signficant temperatures for cell II and cell III crystalstructures are noted on the x-axis with the range of from about 110-122°representing cell II (the type most highly desired in major amounts forfaster processing of the target syndiotactic polypropylene). Cell III isthus represented by temperatures between about 126-131° C. As noted inthe thermogram then, the control exhibits a very low temperature interms of cell II development and a large amount of cell III structures.3,4-DMDBS and NA-11 are very close in their measurements as well.However, the nucleators from Examples 1 and 2 clearly show not only ashift in the temperature for cell II (thus indicating a larger amount),the peaks for cell II are either roughly even with or far in excess ofthose for cell III crystal structures. The actual amounts of suchcrystal structures were thus estimated through triangulation of the peakareas and are tabulated below in Experimental Table 2:

EXPERIMENTAL TABLE 2 Amounts of Cell II and Cell III Crystal Structuresin s-PP with Various Nucleating Agents Nucleator Amount Cell II (%)Amount Cell III (%) Control 25 75 3,4-DMDBS 29 71 NA-11 32 68 Example 248 52 Example 1 65 35

Thus, the inventive sPP containing Example 1 and 2 exhibited far more ofthe desired Cell II form than those of the nucleators known in the art.

Having described the invention in detail it is obvious that one skilledin the art will be able to make variations and modifications theretowithout departing from the scope of the present invention. Accordingly,the scope of the present invention should be determined only by theclaims appended hereto.

1. A thermoplastic comprising between 70-75% syndiotactic polypropylene,wherein said thermoplastic exhibits a crystallization temperature of atleast 71° C. when tested pursuant to a modified ASTM Test MethodD-794-85, wherein the cooling rate is 20° C./min.
 2. The thermoplasticof claim 1 wherein said crystallization temperature is at least 74° C.